What is the difference between fax relay and pass-through ?
Router(config-dial-peer)#fax protocol ?
cisco Use Cisco proprietary protocol
none No FAX protocol
pass-through Use an audio codec for fax transport
system Use choice specified in global fax protocol CLI
t38 Use T.38 protocol
Relay : Cisco and T38
pass-through : Use an audio codec for fax transport
None : disable both mode
with path-through you will use more bandwidth than fax relay because it will use G711